Concrete mishap

[joubjonn]

Just an FYI to any of us who try and torch on concrete. I made a very stupid mistake

I placed my clay with the gold sponge outside on my concrete slab we had poured a few years ago by a landscaping company. I started to heat around the clay with a mapp torch and a few seconds into it a 1/16in layer of cement exploded up into my face. I was wearing safety glasses and didn't do any damage to my face. Just my ego. That was stupid. I should of known better being an engineer. The crucible shot up and cracked, i got very lucky in that I actually found the gram of powder still clumped up like packed clay a few inches away. Recovered almost all of it and did successfully melt it. Just an FYI. If I had not been wearing those glasses I could of lost an eye easy.

 

[GotTheBug]

I see firebrick in your immediate future. Also, to add a .02, probably not a good idea to use any stone high in quartz either, like most granites, etc. The quartz in any stone will do much the same if heated quickly. One of the best ways to give cut stone a "natural" edge is to flame it with a cutting torch, breaking away the surface area by intentional small quartz "explosions".

 

[necromancer]

sorry that i have to say this but......
as an engineer you should have known concrete is hydrophilic.

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hy•dro•phil•ic
adj.
having a strong affinity for water; readily absorbing water.
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thank you for bringing this safety matter to the attention of all forum members.

 

[g_axelsson]

It has nothing to do with any bound water in the concrete, if it was the water then the surface would disintegrate first, not the inside. The "explosion comes from the compression created by the thermal expansion. I've done the same thing with a rock in my youth. I didn't wear any goggles but I closed my eyes just in time and came out of it with a small blister on my eyelid! :shock:

... and I'm an engineer too!

Göran

 

[joubjonn]

i knew what it was immediatly, exactly when it happened, the air inbetween the layer super heated, or heated very quickly and expanded such that the top layer of concrete between the air pocket and the slab blew up in my face. i felt very stupid after that. atleased i found the gold sponge, can't believe i did, since it's so heavy it didn't go far and some how stayed together. fire brick coming soon.

it's just like making clay pots in a kiln, you have to roll that clay to get all the big air pockets out or it will crack in the kiln. you will have some very small air pockets left in the clay. try heating a clay flower pot or dish from home depot with a torch. it will crack if heated quickly. otherwise we would have some cheap melting dishes available from the hardware store.

 

[Irons]

Store the Fire Brick in a dry place as it can absorb Water and do the same. Any porous Ceramic will spall if damp.. Good reason to bake out any moisture before using it.